1. Field of the Invention
The present invention generally relates to tunable inductor circuit and phase tuning circuit utilizing tunable inductor circuit for dynamically tuning signal phase in RF/Microwave circuits and related applications.
2. Description of the Related Art
RF and microwave circuits are widely used in a variety of applications including portable communication devices, such as wireless messaging devices and cellular phones. In many of these applications, power amplifiers are used in the radio receiver that require precise control of signal phase delay.
However, the performance of RF and microwave circuits is highly sensitive to small variations in the analog circuit parameters and to the environment in which they are operated. Small variations of the analog circuit parameters are inevitable as they result from internal defects due to manufacturing processes or from external conditions such as temperature and humidity variations in the operating environment. In a phase delay network, precise control of the signal phase delay is difficult due to the sensitivity of analog circuit parameters to these small variations. Additionally, analog circuits used in portable communication devices often lack a tuning circuit that is capable of compensating for the changing environment due to size and cost considerations.
Efforts have been made in the art to provide tunable devices and tuning circuits that can be implemented in RF and microwave circuits to limit the negative impact of the small variations in the circuit parameters and to improve the performance of these circuits. One improvement is to use a voltage variable capacitor in place of a fixed capacitor in a circuit. Because a voltage variable capacitor provides a range of different capacitance values, a circuit utilizing the voltage variable capacitor provides a tunable capacitive reactance to voltage signals that are applied to the circuit. However, the voltage variable capacitor itself has limited applications because it can only provide a tunable capacitive reactance.
A much wider range of applications can be realized if a suitable tunable inductor is available. Unfortunately, due to the nature of the magnetic fields, currently available tunable inductors are bulky, expensive, and especially impractical to be used in portable communication devices. Consequently, feasible dynamic control of the phase of a signal is not available in many RF and microwave circuits and related applications.